Fixing arrangement with damping for a device which is protected from vibration

ABSTRACT

A fixing arrangement with damping for fixing a device (1) to be protected from vibration, which device includes at least one mounting portion via which the device is fixed to a portion of a support (2) by fastening means (3, 4). The arrangement includes at least two piezoelectric elements (5, 6), each of which has its electrodes electrically shunted by an individual or shared impedance of determined structure. At least one of the elements (5) is used in bending and is interposed between a portion of the support and a mounting portion of the device to be protected. At least one of the elements (6) is used in compression and is interposed between one of the fastening means and either the support portion or the mounting portion.

The present invention relates to a fixing arrangement with damping for adevice liable to be subjected to vibration from which it needs to beprotected, in particular to prevent resonance phenomena from appearing,such resonance causing disturbance and possibly damage.

Such an arrangement is, for example, organized to fix a solar panel, asatellite antenna, or a reflector deployment arm to a support.

BACKGROUND OF THE INVENTION

There exist numerous fixing arrangements, in particular mechanical andelectromechanical fixing arrangements, intended to prevent, or failingthat, to damp either vibration of the devices that they fix together, orvibration that is produced at the device or at the supports therefor andthat can be transmitted from the devices to the supports or vice versa.

Certain types of vibration can disturb and sometimes damage the devicesand/or the supports that they affect, in particular when they give riseto resonance phenomena. Thus, for example, there is a major risk of aplanar satellite antenna structure being destroyed by resonance onlaunching the spacecraft serving to put it into orbit, when alow-frequency vibration is transmitted to it via its support and/oracoustically.

To avoid such drawbacks, attempts are made firstly to apply treatmentdirectly by damping at the device that needs to be protected against thevibration, and secondly to decouple the vibration source(s) from thedevice to be protected.

One conventional solution for providing such decoupling consists ininterposing passive damping means, such as elastomer washers between adevice and its support. Unfortunately, although that solution is veryeffective against high-frequency and medium-frequency vibration, itsuffers from the drawback of tending to amplify the movements caused byvibration whose frequency is low. When the vibration is at frequenciesdistributed over a wide band, it is then necessary to associate thepassive damping means with non-linear displacement-limiting means and/oractive control means.

It is known that piezoelectric materials such as PZT or PVDF can be usedin passive vibration-damping arrangements.

It is also known that a piezoelectric element having electrodes shuntedby an inductive circuit behaves as if it were viscoelastic and it thenhas a damping factor that is similar to the damping factors ofviscoelastic materials and that varies as a function of frequency and asa function of the electrical characteristics of the shunt circuit for agiven element.

Document EP-A-0 375 370 describes a method of conditioning apiezoelectric element. That method makes it possible to cause thestiffness of the element to vary significantly by acting on a capacitorincluded in a resistive circuit via which electrodes provided in theelement are shunted. It recommends implementing that method in dampingarrangements. However, the damping factor that can be obtained for apiezoelectric element working in bending is considerably lower than thedamping factor that can be obtained with elements made of viscoelasticmaterials.

That method does not make it possible to implement a fixing arrangementthat offers both high rigidity and a good damping factor for fixing adevice to a support when the device needs to be protected fromvibration.

SUMMARY OF THE INVENTION

The present invention therefore proposes a fixing arrangement withdamping for fixing a device that is to be protected from vibration, thefixing arrangement making it possible, in particular, to damp resonancethat can occur at the device and in the low-frequency range.

The arrangement comprises at least one "mounting" portion via which thedevice is fixed to a support by fastening means, and at least onepiezoelectric element which has electrodes shunted electrically by animpedance that is of a determined structure and that is in an interfaceposition between the support and a mounting portion of determineddimensions.

According to a characteristic of the invention, the arrangementcomprises at least two piezoelectric elements, each of which has itselectrodes electrically shunted by an individual or shared impedance ofa determined structure, with at least one of the elements being used inbending and being interposed between a portion of the support and amounting portion of the device to be protected, and at least one elementbeing used in compression and being interposed between one of thefastening means and either the support portion or the mounting portion.

According to a characteristic of the invention, the arrangement includesa piezoelectric element used in bending and implemented in the form of aplate that is dimensioned and positioned so as to extend beyond at leastone of the portions against which it is secured, namely either themounting portion or the support portion.

According to a characteristic of the invention, the arrangementcomprises at least one piezoelectric element used in compression andimplemented in the form of a washer positioned between either a supportportion or a mounting portion and fastening means for fastening themounting portion to the support portion, the washer being mounted arounda stem serving as a clamping intermediary included either in thefastening means, or in additional fastening means.

According to a characteristic of a variant of the invention, thearrangement comprises a plurality of piezoelectric elements used inbending and forming a stack of plates, a first one of the plates beingsecured against a mounting portion or a support portion, the stack beingdimensioned and positioned so as to extend beyond the mounting portionor the support portion against which the first plate of the stack issecured.

According to a characteristic of a variant of the invention, thearrangement comprises at least one piezoelectric element used incompression and implemented in the form of a stack of washers positionedbetween either a support portion or a mounting portion and fasteningmeans for fastening the mounting portion to the support portion, thestack being mounted around a stem serving as a clamping intermediaryincluded either in the fastening means or in additional fastening means.

According to a characteristic of the invention, the arrangement includesfastening means of the nut-and-bolt type having at least one bolt stemwhich passes both through a piezoelectric element of the washer or stackof washers type, and through a piezoelectric element of the plate type,provided with a through opening for receiving each bolt.

The invention, its characteristics, and its advantages are described inmore detail in the following description given with reference to thefigures listed below:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is diagram of a circuit using a known principle for electricallyconnecting a piezoelectric element for a damping arrangement;

FIG. 2 shows a first embodiment of an arrangement of the invention;

FIG. 3 shows a second embodiment of an arrangement of the invention; and

FIG. 4 shows a third embodiment of an arrangement of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The arrangement of the invention is assumed to include a conventionalelectric circuit, comprising a set of one or more piezoelectricelements, and referenced 0 in FIG. 1. A passive or preferably an activeimpedance, referenced Z, is connected across the terminals of thecircuit. One of the terminals that is common to the set of piezoelectricelements and to the impedance is connected to a ground potential, as isknown. An electric circuit of this type is assumed to be provided ineach of the arrangements of the invention, and it is not shown inaccompanying FIGS. 2 to 4 insofar as it is only indirectly related tothe invention.

The arrangement of the invention shown in FIG. 2 is designed to fix adevice 1 to a support 2, the device being liable to be subjected tovibration from which it needs to be protected.

For example, the device may be constituted by satellite antenna panel,or by a solar panel. It includes at least one "mounting" portion whichis the only portion shown in the figures, and via which it is fixed to aportion of the support 2, shown in the form of a stand-type element. Thedevice is fixed to the support via a fixing arrangement with dampingthat is optionally constituted in modular manner if the device includesa plurality of mounting portions, each of which corresponds to arespective portion of the support.

In the examples shown, a single mounting portion is shown for the device1 in question, and as is known, provision is made to use piezoelectricelements in combination with fastening means for implementing thevibration-damping fixing arrangement of the invention.

Fastening the mounting portion of the device 1 to a portion of thesupport 1 is shown by way of example as being achieved by firstfastening means, such as a bolt 3, co-operating with second meanscomplementary to the first means, such as complementary tapping 4,assumed in this example to be provided in the mounting portion of thedevice 1.

Naturally, other fastening means may be implemented to procureequivalent effects, as shown in particular in FIGS. 3 and 4 in which anut 4' is implemented in co-operation with a bolt 3' to obtain theclamping effect that can also be obtained by the fastening meansconstituted by the tapping 4 and the bolt 3.

In accordance with the invention, and as shown in particular in FIG. 2,a piezoelectric element 5, assumed in this example to be implemented inthe form of a plate designed to work in bending, is interposed betweenthe mounting portion of the device 1 in question and that portion of thesupport 2 to which the mounting portion is fixed. An insulatingseparator (not shown) is provided between the plate which constitutesthe element 5 and one of the two portions between which it is interposedand against which it bears via its two large faces. The element 5 isassumed in this example to be grounded by being in contact with that oneof the two portions against which it bears directly, without theinsulating separator being interposed, if, as assumed in this example,the device 1 and the support 2 are themselves grounded at least at thetwo portions that are assumed to be conductive and that are consideredabove.

For example, the plate which constitutes the piezoelectric element 5 maybe made of one or more layers of a material such as PZT or PVDF, asindicated above, and it is designed to damp any bending of the devicewhere the mounting portion of the device is fastened to thecorresponding portion of the support.

In one embodiment, the plate which constitutes the piezoelectric element5 extends beyond at least one of the two portions, namely the mountingportion of the device 1 and the portion of the support 2, between whichportions the plate is interposed.

In the embodiment shown in FIG. 2, in which that portion of the supportto which the device is fixed is assumed to be of the stand typeincluding an enlarged seat, the plate extends beyond said seat. In manycases, the device 1 can have dimensions considerably larger than thedimensions of the seat of the support 2 to which it is fixed.

In a variant of the invention (not shown), provision is made to replacethe single piezoelectric element 5 shown in FIG. 2 with a stack ofpiezoelectric elements used in bending, thereby enabling the voltageapplied to each element to be divided in proportion to the number ofelements in the stack compared with the case when a single element isimplemented.

In accordance with the invention, and as shown in particular in FIG. 2,provision is made to associate at least one other piezoelectric element6, assumed in this example to be implemented in the form of at least onewasher designed to work in compression, it being understood that theterm "washer" covers any part performing an equivalent function. Eachwasher corresponds to a different piezoelectric element 6 and is assumedin this example to be interposed between that portion of the support 1against which the piezoelectric element 5 as considered above bears, andone of the fastening means, i.e. in this example the bolt 3, or moreprecisely the head of this bolt 3 which fixes the device 1 to thesupport 2. Once the device is fastened to the support by bolting, such awasher as threaded over the stem of the corresponding bolt 3 is heldbetween the head of the bolt and the portion of the support 2 throughwhich said bolt passes to screw into the tapping 4 provided for it inthe mounting portion of the device 1.

Naturally, in numerous embodiments (not shown), a plurality ofpiezoelectric elements 6 may be associated with the same piezoelectricelement 5 at a fixing module for fixing one or more mounting portions ofa device to one or more corresponding portions of a support. Such aconfiguration being symbolized by the presence of an axis disposedsymmetrically relative to the bolt 4 about the axis of the support stand2, 2', 2" in FIGS. 2 to 4.

In the embodiments considered, each bolt passes through the plateconstituting the piezoelectric element 5 so as to screw into the tapping4 in the mounting portion of the device 1.

In a variant embodiment shown in FIG. 3, the arrangement includes apiezoelectric element 5' corresponding to the piezoelectric element 5shown in FIG. 2, but each piezoelectric element 6' which corresponds toan element 6 of FIG. 2 is, in this example, clamped against the head ofa bolt 3' which is accessible from the other side of the mountingportion of the device 1' relative to the piezoelectric element 5' andrelative to the support 2'. Each bolt 3' presses a piezoelectric element6' through which it passes against the mounting portion of the device,through which portion its stem also passes. The stem also passes throughthe support portion 2' to which said mounting portion is fixed so as tomake it possible to screw on a clamping nut 4' that performs a functionanalogous to the function of the tapping 4.

In another variant embodiment shown in FIG. 4, the arrangement includesa piezoelectric element 5" corresponding to the piezoelectric element 5shown in FIG. 2, but each piezoelectric element 6" which corresponds toan element 6 of FIG. 2 is, in this example, constituted by a stack ofwashers through which a bolt stem 3" passes. Each bolt 3" is assumed inthis example to be associated with a nut 4" in a mounting configurationcorresponding to the configuration provided for a screw 3' and a nut 4'in the variant shown in FIG. 3. The stack which constitutes thepiezoelectric element 6" then passes through the piezoelectric element5" at an opening provided for the bolt 3", and it then comes directlyinto abutment against that portion of the support 1 to which themounting portion of the device 1 is fixed, when the nut 4" is screwed tothe bolt 3" so as to fasten the device to the support in the region ofthe nut and bolt.

In a variant embodiment, a calibrated spring (not shown) may optionallybe placed between the head of the bolt 3 and the closer end washer inthe stack so as to facilitate pressure adjustment. The washersconstituting the piezoelectric elements 5, 5' and the stack constitutingthe piezoelectric element 5" make it possible to damp the bending of thedevice 1 by being compressed in the direction of their respectivethicknesses, which direction is perpendicular to the electrodes providedat the ends of these elements.

The elements thus present a high damping potential because thecorresponding mechanical-to-electrical conversion coefficient "k33" ishigher than 0.7, and is therefore high. The plate constituting thepiezoelectric element 6, 6', or 6" has a coefficient "k31" that is lessthan 0.4 and is therefore significantly lower, this being compensated bythe large area of the plate.

Each of the above-mentioned piezoelectric elements is connected toground potential by one electrode, and is insulated from said potentialby means of the insulating separator at another electrode, as indicatedabove. As known to the person skilled in the art, the other electrode(s)is/are connected to one or more active or passive impedances of a givenstructure, making it possible to shunt the elements either individuallyor in parallel depending on the choices made.

Shunting by a resistor alone makes it possible to obtain a small amountof damping over a broad band. The lower the capacitance of thepiezoelectric element, the greater the damping.

Implementing an impedance made up of a resistor and of a passive or anactive inductor, and made, for example by associating high-voltageamplifiers, makes it possible to control resonance.

It is also possible to use a multimode resonant electric circuitoptionally associated with a circuit, making it possible to vary thecapacitance of a piezoelectric element across the terminals of which themultimode resonant circuit is placed.

Any variations in the dynamic range of the device 1 to be protected, andin particular resonance, can be taken into account by adjusting theresistors and the inductors which are adjusted by means of resistorswhich are themselves adjustable. The initial adjustment is preferablymodified in real time as a function of the variations in the vibrationfrequencies over time, which frequencies are determined by appropriatesignal-processing means which are not described in any more detailherein insofar as they are related only indirectly to the presentinvention.

What is claimed is:
 1. A fixing arrangement with damping for fixing adevice to be protected from vibration, the device which includes atleast one "mounting" portion via which the device is fixed to a portionof a support by a nut-and-bolt fastening mechanism, said arrangementcomprising:a plurality of piezoelectric elements, each of which has itselectrodes electrically shunted by either one of an individual and ashared impedance of determined structure, with at least one of thepiezoelectric elements being used in bending and being interposed at anut end of said nut-and-bolt fastening mechanism directly between aportion of the support and a mounting portion of determined dimensions,of the device to be protected, and at least another one of thepiezoelectric elements being used in compression and being interposedbetween a bolt end of said nut-and-bolt fastening mechanism and thesupport portion.
 2. A fixing arrangement according to claim 1, whereinsaid one of the piezoelectric elements used in bending is implemented ina form of a plate that is dimensioned and positioned so as to extendbeyond at least the portion against which it is secured, namely eitherone of the mounting portion and the support portion.
 3. A fixingarrangement according to claim 1, wherein at least one of saidpiezoelectric elements used in compression is implemented in a form of awasher positioned between either one of a support portion and a mountingportion and said nut-and-bolt fastening mechanism for fastening themounting portion to the support portion, said washer being mountedaround a stem serving as a clamping intermediary included in either oneof the fastening mechanism and in additional fastening mechanisms.
 4. Afixing arrangement according to claim 1, wherein the nut-and-boltmechanism includes at least one bolt stem which passes both through apiezoelectric element of either one of a washer type and stack ofwashers type, and through a piezoelectric element of a plate type,provided with a through opening for receiving each said bolt, and a nutwhich is screwed onto said bolt to fix said device.
 5. A fixingarrangement with damping for fixing a device to be protected fromvibration, the device which includes at least one "mounting" portion viawhich the device is fixed to a portion of a support by fastening means,said arrangement comprising:a plurality of piezoelectric elements, eachof which has its electrodes electrically shunted by either one of anindividual and a shared impedance of determined structure, with at leastone of the piezoelectric elements being used in bending and beinginterposed between a portion of the support and a mounting portion ofdetermined dimensions, of the device to be protected, and at leastanother one of the piezoelectric elements being used in compression andbeing interposed between one of the fastening means and either one ofthe support portion and the mounting portion; wherein said plurality ofpiezoelectric elements used in bending forms a stack of plates, a firstone of the plates being secured against either one of a mounting portionand a support portion, said stack being dimensioned and positioned so asto extend beyond one of the mounting portion and the support portionagainst which the first plate of the stack is secured.
 6. A fixingarrangement with damping for fixing a device to be protected fromvibration, the device which includes at least one "mounting" portion viawhich the device is fixed to a portion of a support by fastening means,said arrangement comprising:a plurality of piezoelectric elements, eachof which has its electrodes electrically shunted by either one of anindividual and a shared impedance of determined structure, with at leastone of the piezoelectric elements being used in bending and beinginterposed between a portion of the support and a mounting portion ofdetermined dimensions, of the device to be protected, and at leastanother one of the piezoelectric elements being used in compression andbeing interposed between one of the fastening means and either one ofthe support portion and the mounting portion; wherein at least one ofsaid piezoelectric elements used in compression is implemented in theform of a stack of washers positioned between either one of a supportportion and a mounting portion and the fastening means for fastening themounting portion to the support portion, said stack being mounted arounda stem serving as a clamping intermediary included in either one of thefastening means and in additional fastening means.